EP0695938A1 - Procedure for determing the percentage constituent of a material composed of at least two distinct constituents - Google Patents

Abstract

A differential calorimeter is used to produce graphs relating rate of heat transference to time. The graphs comprise a baseline (LB), a curve (CC1) for a first known constituent of the sample and a curve (E1) for the sample. The thermal capacity of the sample (CPEI) is first determined using masses analysed, known thermal capacity of the first constituent and the ratio of surfaces (A1,C1,C1l,A1') and A1',B1,B1',A1') cut off by vertical intercepts of the graphs. The percentage of the first constituent in the sample is then found from the ratio of the difference in first constituent and sample thermal capacities to the difference of the two constituents thermal capacities.

Description

During the production of a certain number of materials comprising at least two constituents, it is useful to know the composition of the material during its preparation, in order to be able to obtain the material corresponding precisely to the intended use. This is the case, for example, of steels, or more generally of metal alloys. This is also the case for composite materials consisting of a plastic resin within which are placed reinforcing fibers.

With regard to metallic alloys, a method of observing the temperature of the molten alloy is known, in particular the lowering of the solidification temperature of the alloy as a function of the percentage of additional elements added to determine this percentage. Determinations of percentages of constituents by this process are generally long, difficult to implement, even dangerous. Other methods exist, - chemical, by acid attacks, or, physical, by pyrolysis, measurements of volume, or density -, and generally have similar drawbacks and for some do not take the porosities into account.

There is therefore a need to be able to determine the percentages of the composition of a material comprising several constituents, quickly and easily. This is particularly evident with regard to the fiber content of composite plastic materials.

The purpose of the proposed method is to satisfy the existing need and is therefore essentially a method of determining the percentage of a constituent of a material composed of at least two distinct constituents.

According to the method according to the invention, the thermal capacity of a sample of said material or a physical quantity proportional to this thermal capacity is determined, and, from knowledge of the thermal capacity of each of the two said constituents or of said quantity which is proportional to it, a first difference is calculated between the thermal capacities of the sample and of said constituent or between said physical quantities which are respectively proportional thereto, and a second difference between the thermal capacities of the two said constituents of the material or between said physical quantities which are respectively proportional to it, and, the percentage of said constituent is determined by calculating the ratio of the first to the second difference.

• pour déterminer la capacité thermique dudit échantillon, on établit la correspondance entre la température d'une première masse de l'échantillon et d'une deuxième masse munie dudit constituant, et, lesdites grandeurs physiques qui sont respectivement proportionnelles à leurs capacités thermiques, puis, pour une température déterminée, on mesure lesdites grandeurs physiques, et, enfin, on détermine la capacité thermique massique de l'échantillon en calculant le rapport d'un premier produit de ladite grandeur physique relative à l'échantillon, par ladite deuxième masse du constituant, par la capacité thermique connue du constituant à un deuxième produit de ladite grandeur physique relative audit constituant par ladite première masse de l'échantillon;
• on acquiert la connaissance de la capacité thermique de chacun desdits constituants ou de ladite grandeur physique qui y est proportionnelle, en réalisant une détermination analogue à celle de la capacité thermique dudit échantillon ou de la grandeur physique qui y est proportionnelle;
• on établit la correspondance entre la température d'une même masse déterminée de chacun desdits constituants et de l'échantillon, et, lesdites grandeurs physiques qui sont respectivement proportionnelles à leurs capacités thermiques, puis, pour une température déterminée, on mesure lesdites grandeurs physiques, et enfin, on détermine ledit pourcentage d'un desdits constituants du matériau en calculant le rapport de la différence des grandeurs physiques relatives à l'échantillon et audit constituant à la différence des grandeurs physiques relatives aux deuxdits constituants.

The following advantageous arrangements are also preferably adopted:

• to determine the thermal capacity of said sample, the temperature between a first mass of the sample and a second mass provided with said constituent is established, and said physical quantities which are respectively proportional to their thermal capacities, then, for a determined temperature, said physical quantities are measured, and finally, the mass thermal capacity of the sample is determined by calculating the ratio of a first product of said physical quantity relative to the sample, by said second mass of the constituent , by the known thermal capacity of the constituent to a second product of said physical quantity relative to said constituent by said first mass of the sample;
• acquiring knowledge of the thermal capacity of each of said constituents or of said physical quantity which is proportional thereto, by carrying out a determination analogous to that of the thermal capacity of said sample or of the physical quantity which is proportional thereto;
• the correspondence between the temperature of the same determined mass of each of said constituents and of the sample is established, and said physical quantities which are respectively proportional to their thermal capacities, then, for a determined temperature, said physical quantities are measured, and finally, said percentage of one of said components of the material is determined by calculating the ratio of the difference of the physical quantities relating to the sample and to said component to the difference of the physical quantities relating to the two said components.

The main advantage of the methods in accordance with the invention resides in the ease and speed of their implementation, by the use of differential calorimeters, preferably associated with calculating machines, then constituting specialized apparatus capable, from a single measure, to determine the percentage sought.

The invention will be better understood and secondary characteristics and their advantages will become apparent during the description of two embodiments given below by way of example.

It is understood that the description and the drawings are given for information only and are not limiting.

Reference will be made to the appended drawings, in which FIGS. 1 and 2 represent the curves recorded according to two variant methods according to the invention.

The two examples of implementation of the method according to the invention are explained with reference to FIGS. 1 and 2.

, dérivée de la quantité de chaleur transférée à un matériau par rapport au temps, en millicalorie/seconde. Dans les exemples représentés, le calorimètre différentiel utilisé était le type DSC4 du fabricant PERKIN-ELMER.The main device used is a differential calorimeter which allows the recording of the curves represented in the variation figures as a function of the temperature T in degree C of the function. $$\frac{\text{dQ}}{\text{dt}}$$

, derived from the amount of heat transferred to a material over time, in millicalories / second. In the examples shown, the differential calorimeter used was the DSC4 type from the manufacturer PERKIN-ELMER.

• Vitesse de montée de température:   20°C/mn
• Vitesse de refroidissement:   320°C/mn
• Température initiale:   70°C
• Température finale:   90°C
• Unités:   millicalorie ou milliwatt
• Echelle:   2 milliwatts
• Sans remise au zéro électrique du signal du calorimètre:   R.A.Z NON
• Réglage du zéro électrique:   ZERO
• Masse de l'échantillon:   20mg
• Tracé en temps réel des courbes de CP.

During a preliminary phase of the process, the following parameters were first recorded:

• Temperature rise speed: 20 ° C / min
• Cooling rate: 320 ° C / min
• Initial temperature: 70 ° C
• Final temperature: 90 ° C
• Units: millicalorie or milliwatt
• Scale: 2 milliwatts
• Without electrical reset of the calorimeter signal: RESET NO
• Electric zero adjustment: ZERO
• Sample mass: 20mg
• Real-time plotting of CP curves.

The indicated values of temperature rise rate and cooling rate and mass of the sample are indicative values. Those of the initial and final temperatures were chosen so that the thermal capacities CP are substantially constant.

The choices of "without electrical reset", "electrical zero adjustment" and "real-time plotting" of the thermal capacity curves have been carried out to take into account the fact that the device used did not allow the recording of several curves (3 in the examples described) of thermal capacities while preserving the same electrical zero of the signal. It was therefore necessary to record in real time the curves which otherwise would not have been saved. The adopted measurement procedure thus allows the superimposition of the curves during the analyzes.

The material samples of which it is desired to know the composition are analyzed one after the other, without carrying out a reinitialization of the apparatus between two analyzes, the curves therefore being plotted in real time.

According to the first method described with reference to FIG. 1, a base line LB is acquired and specific to the device used. The curves CC1 and EI are recorded and correspond, one CC1 to a first known constituent of the material, the other EI to a sample of the unknown material. These three curves allow the calculation of the thermal capacity CPEI of the sample of the unknown material, and to deduce therefrom the percentage of the first known constituent that it contains. It is specified that, according to this first method, the masses analyzed MCC1 of the first known constituent and MEI of the sample (the percentage of which in the first constituent is unknown) of the material may have different values, CPCC1 being the thermal capacity , known, of the first known constituent of the material of which the percentage is sought, and, A1 B1 C1 and A1 'B1' C1 'being two lines parallel to the ordinate axis, corresponding to temperatures T1, T1', intersecting the curves LB, CC1 and EI at points A1, B1, C1, and, A1 ', B1', C1 ', respectively, the expression used to calculate CPEI first is as follows: $$\text{CPEI =}\frac{\text{(area A1 C1 C1 'A1') x MCC1}}{\text{(area A1 B1 B1'A1 ') x MEI}}\text{x CPCC1}$$

The percentage PCC1 of the known constituent CC1, which the sample of the material EI contains, is proportional to 100 times the ratio of the absolute value of the difference | CPCC1-CPEI | thermal capacities of the first known constituent and the sample of the unknown material divided by the absolute value of the difference | CPCC1-CPCC2 | known thermal capacities of the first and second known constituents of said material: $$\text{PCC1 =}\frac{\text{| CPCC1-CPEI |}}{\text{| CPCC1-CPCC2 |}}\text{x 100}$$

According to the second method described with reference to FIG. 2, it is possible to determine the percentage PCC1 of the known constituent CC1 that the sample of the unknown material EI contains without first knowing the thermal capacities CPCC1 and CPCC2 of the first and second constituents of said material . On the other hand, it is necessary to have samples of equal masses of each of the two known constituents and of the unknown material. It then suffices to record the three curves relating to the two known constituents CC1 and CC2, and, that relating to the unknown material EI. A2 B2 C2 and A2 'B2' C2 'being two parallel lines, corresponding to temperatures T2, T2', at the data axis, intersecting curves CC2, EI and CC1 at points A2, B2, C2 and A2 ', B2 ', C2', respectively, the expression used to calculate the percentage PCC1 of the first constituent contained in the unknown material is as follows: $$\text{PCC1 =}\frac{\text{surface (B2 C2 C2'B2 ')}}{\text{surface (A2 C2 C2 'A2')}}\text{x 100}$$

As a variant, it is also possible to program, in any order, a rise in temperature of the calorimeter, and a leveling off. The jump in the curve observed when passing from one measurement phase to the other is proportional to the thermal capacity, to within a corrective factor, and is capable of replacing the lengths of the segments of the lines A2 B2 C2, A2 ' , B2 ', C2', cut on these lines by the curves CC1, CC2 and EI.

The previous examples correspond to actual measurements made using the "PERKIN-ELMER" differential calorimeter. It is possible to optimize the methods described by preferably using only one measurement. According to this last variant, the baseline is acquired by means of a internal calibration, which the device has, and the values of the known thermal capacities CC1 and CC2 of the first and second known constituents of the material are introduced from a computer keyboard, or else are stored beforehand. With such an apparatus constituted by a differential calorimeter and an associated computer, it remains naturally possible, in the case where the thermal capacities CPCC1 and / or CPCC2 are not known beforehand, to measure them by means of the apparatus itself during preliminary measurements.

The processes which have just been described, and the apparatuses which allow their implementation, are particularly well suited to determining the percentage of resins and fibers contained in the composite materials, these percentages usually characterizing the finished products.

While the methods known to date (chemical methods by acid attacks, physical methods by pyrolysis, or measurements of volumes or densities) are often long (several hours) and sometimes, for some of them unusable (acid attack , as pyrolysis attack for example the two constituents fibers and organic matrix of a composite material), the new claimed methods allow rapid determinations (5 minutes), and receive all the applications in which the thermal capacities of the constituents are different; moreover, the samples can have small dimensions (of the order of a gram, or even less than a gram), can also have irregular shapes, which is an advantage compared to certain known methods according to which the thickness of the the sample is measured.

The invention is not limited to the embodiments described, but on the contrary covers all the variants which could be made to them without departing from their scope or their spirit.

Claims (4)

Method for determining the percentage (PCC1) of a constituent (CC1) of a material (EI) composed of at least two distinct constituents (CC1, CC2),
characterized in that the thermal capacity (CPEI) of a sample (EI) of said material is determined or a physical quantity proportional to this thermal capacity, and, from knowledge of the thermal capacity (CPCC1, CPCC2) of each of said two components (CC1, CC2) or of said physical quantity which is proportional thereto, a first difference (CPCC1-CPEI) is calculated between the thermal capacities of the sample (EI) and of said constituent (CC1) or between said physical quantities which are respectively proportional to it, and, a second difference (CPCC1-CPCC2) between the thermal capacities of the two said constituents (CC1, CC2) of the material or between said physical quantities which are respectively proportional thereto, and, the percentage is determined (PCC1) of said constituent (CC1) by calculating the ratio of the first to the second difference. Method according to claim 1,
characterized in that, to determine the thermal capacity (CPEI) of said sample (EI), the correspondence (CC1, CC2, EI) is established between the temperature of a first mass (MEI) of the sample and of a second mass (MCC1) of said constituent, and, said physical quantities which are respectively proportional to their thermal capacities, then, for a determined temperature (T1, T1 ′), said physical quantities are measured, and finally, the mass thermal capacity is determined ( CPEI) of the sample by calculating the ratio of a first product of said physical quantity relative to the sample (EI), by said second mass (MCC1) of the constituent, by the known thermal capacity (CPCC1) of the constituent to a second product of said physical quantity relative to said constituent (CC1) by said first mass (MEI) of the sample. Method according to claim 1,
characterized in that one acquires knowledge of the thermal capacity (CPCC1, CPCC2) of each of said constituents or of said physical quantity which is proportional thereto, by carrying out a determination analogous to that of the thermal capacity (CPEI) of said sample (EI ) or the physical quantity which is proportional to it. Method according to claim 3,
characterized in that the correspondence is established between the temperature (T) of the same determined mass of each of said constituents (CC1, CC2) and of the sample (EI), and, said physical quantities which are respectively proportional to their thermal capacities, then, for a determined temperature (T2, T2 '), said physical quantities are measured, and finally, said percentage (PCC1) of one (CC1) of said constituents of the material is determined by calculating the ratio of the difference | CPCC1-CPEI | physical quantities relating to the sample and said constituent unlike physical quantities relating to the two said constituents | CPCC1-CPCC2 |.

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